There are known plasma thrusters or "accelerators" with a closed electron drift which are used for various technical applications. See L. Artsimovitch, "Plasma accelerators", Moscow, Mashinostroenie, 1974, pp. 54-95.
One such accelerator with closed electron drift has an extended accelerator region (ACEDE: Accelerator with Closed Electron Drift that has an extended acceleration region) and comprises a dielectric discharge chamber with an annular accelerating channel, the exit part of which is between two magnetic poles. This accelerator also includes an anode-gas distributor located deep inside the accelerating channel. See L. Artsimovitch, "Plasma accelerators", Moscow, Mashinostroenie, 1974, pp. 75-81. Another accelerator of ACED type is known as an anode layer accelerator (ALA). It has a metal discharge chamber and a shortened acceleration region.
The main difference between ACEDE and ALA is that ACEDE accelerators have a fundamentally nonuniform magnetic field in a relatively long accelerating channel, the walls of which limit accelerated plasma flow. See A. Bober, V. Kim, et al., "State of Work on Electrical Thrusters in the USSR", AIAA Paper IEPC-91-003, 6 pp. The following ratios define ACEDE and ALA parameters: EQU ACEDE:L.sub.C /L.sub.B .about.1,L.sub.C /b.sub.C .gtoreq.1,b.sub.O /b.sub.C .about.1 EQU ALA:L.sub.C /L.sub.B &lt;1,L.sub.C /b.sub.C &lt;1,b.sub.O /b.sub.C &lt;1(1)
Where:
L.sub.C and L.sub.B are the length of the accelerating channel and length of the region with a sufficiently high value of magnetic induction, respectively. PA1 b.sub.C and b.sub.O are the width of the accelerating channel and characteristic radial dimension of the flow in acceleration region, respectively.
The above mentioned differences are significant, as they define differences in the operation processes of the respective accelerators. In particular, potential distribution in the accelerating channels of the ALA accelerator (in both one-stage and two-stage designs) are determined mainly by external voltage sources, and electrode (anode and cathode) positions, defining the lengthwise dimensions of the acceleration stages.
The location of the ionization and acceleration layer (IAL) in the ACEDE accelerator is a function of the magnetic field distribution in the accelerating channel and interaction of the plasma flow with the discharge chamber walls. Thus, unlike ALA accelerators, the distribution of the electric field in the larger part of the ACEDE accelerating channel is created without significant impact of electrodes' positions.
Another known plasma accelerator with a closed electron drift comprises a dielectric discharge chamber with annular external and internal walls to form an accelerating channel, a magnetic system with magnetic field sources, a magnetic path, external and internal magnetic poles to form an operating gap at the exit part of the discharge chamber walls, a gas distributor-anode situated inside the accelerating channel at a distance from the exit plane of the discharge chamber exceeding the width of the accelerating channel, and a cathode-compensator. See A. Bober, V. Kim, et al., "State of Work on Electrical Thrusters in the USSR", AIAA Paper IEPC-91-003, 6 pp. Integral parameters of this device permitted to design thrusters for use on spacecraft and accelerators for ground applications based on its design.
However, the known thruster does not have an efficiency and lifetime sufficient for many missions due to discharge chamber wall sputtering by accelerated ions, and considerable plume divergence. Thus, efficiency of the contemporary ACEDE (type SPT-100) does not exceed 50%, and its lifetime is 7,000 hours at an exhaust velocity of .about.16 km/sec. In this case, plume divergence half angle .beta..sub.0.95 is .about.45.degree. for 95% of accelerated ions in the exhausting flow.
Still another known plasma thruster with a closed electron drift comprises a dielectric discharge chamber with annular external and internal walls to form an accelerating channel, a magnetic system with magnetic field sources, a magnetic path, external and internal magnetic poles, an anode unit with a gas distributor, and a cathode-compensator. In this case, part of one of the walls is made of electric conducting material. See the international patent application WO 94/02738, published Feb 3, 1994, F03H1/00, H05H1/54. The efficiency and lifetime of this plasma accelerator is also limited by insufficient focusing of the ion flow, which also causes significant energy losses and ion sputtering of accelerator components.